1. Field of the Invention
This invention relates to an apparatus for polishing a semiconductor wafer, and especially relates to an apparatus for polishing a semiconductor wafer which is effective to polish uniformly the surface of the wafer with a simple structure.
2. Description of the Prior Art
Conventionally, polishing a semiconductor wafer is conducted according to the following procedure.
1) A semiconductor wafer is contacted to a polishing cloth with a polishing liquid therebetween.
2) The semiconductor wafer is pressed against the polishing cloth by applying a pressure to the semiconductor wafer.
3) The semiconductor wafer is rotated in a state where the pressure is applied.
It is known that the apparatus having the following construction to carry out a series of the above procedure.
1) A disk having a larger diameter than the diameter of the semiconductor wafer.
2) A rotation axis fixed to the center of the disk.
3) A mechanism to press the semiconductor wafer with the bottom surface of the disk by supplying the rotation axis with a driving force.
However, the pressure generated by the driving force concentrates on the vicinity of the center of the disk because the pressure is applied to the disk through the rotation axis. Therefore, the pressure distribution applied from the disk to the wafer is uneven, as a result of which there is a problem that the irregularity occurs on the polishing surface of the wafer.
Unexamined Japanese Patent Publication No. H6-15563 and No. H5-69314 disclose the technologies which are known to solve this problem. In this conventional technologies, the fluid is supplied between the wafer and the disk. Therefore the mechanism for supplying the fluid must be installed in the conventional polishing apparatus.
However, the mechanism to supply the fluid has a complex structure in general. Furthermore, where the disk fixed to the rotation axis is rotated at the high speed, it is difficult to supply the fluid.
An object of this invention is to provide an apparatus for polishing a semiconductor wafer which is effective to polish uniformly the surface of the wafer with a simple structure.
To achieve the above object, this invention is created by paying attention to the aspect that the fluid is housed in the piston structure.
According to this invention, the pressure can be distributed uniformly in the fluid. Consequently, the surface of the wafer is pushed with a uniform pressure.
As a result, the surface of the polished wafer becomes flat.